Long-term Vegetation Monitoring Research Articles

罗山国家级自然保护区森林植被资源监测与分析

根据罗山保护区的典型地带性特点和森林植被资源特点，按照长期定位监测的要求，在保护区设置用于长期定位监测植被变化情况的样地，对罗山的植被资源定位监测，系统分析其植被多样性，为罗山自然保护区科学管理与可持续发展提供依据。结果表明：以草地和灌木地为主的山体共有木本植物32种，草本植物168种。小罗山以草本和灌木植物为主，平均高度分别为16.54 cm和36.69 cm；大罗山植被分布复杂、种类多，植被以草地和灌木地为主的山体物种丰富度在0.007~0.009这之间。罗山大多数植物种多度小于20%，木本灌木的多度大于50%，草本植物种的频度小于40%。调查的几条路线中，物种丰富度指数差异较小。According to the typical zonality and forest vegetation characteristics of Luoshan nature reserve, and long-term located monitoring requirement, we set up sample plots in Luoshan nature reserve for long-term located monitoring of forest vegetation to analyze its dynamic changes and biodiversity that will provide reference for scientific management and sustainable development in Luoshan nature reserve. The result shows that there are 168 herbaceous plants and 32 woody plants for all grassland and shrub plots. The small Luoshan only has herbaceous plants and shrubs, and their average height is 16.54 cm and 36.69 cm respectively. The plants in big Luoshan are more diverse and complex, and species richness of grassland and shrub plots is between 0.007~0.009. The abundances for different plants in Luoshan are less than 20%; the abundances for woody plants are greater than 50%, while frequentness for herbaceous plants is less than 40%. There is no big difference in species richness index of the plots in Luoshan.

Experimental Evaluation of Sentinel-2 Spectral Response Functions for NDVI Time-Series Continuity

Remote sensing of long-term vegetation monitoring relies on the analysis of multisensor and multitemporal time-series measurements. Cross-sensor calibration is therefore important to prevent artifacts in the temporal signal due to inherent differences in sensors configurations. Variations in spectral response functions (SRFs) are among the major causes of differences in multisensor reflectances and products. In this paper, we report on the SRF comparability of the upcoming Sentinel-2 Multispectral Instrument (MSI) sensor with a number of operational sensors National Oceanic and Atmospheric Administration (NOAA)/ Advanced Very High Resolution Radiometer (AVHRR9), Landsat 7 Enhanced Thematic Mapper Plus (ETM+), Satellite Pour l'Observation de la Terre VEGETATION1 (VGT1), Moderate Resolution Imaging Spectroradiometer (MODIS), and Medium Resolution Imaging Spectrometer (MERIS) relevant for vegetation monitoring. SRF cross-sensor calibration methods for the conversion of red and near infrared (NIR) reflectances and Normalized Difference Vegetation Index (NDVI) values of operational sensors in reference to the Sentinel-2 MSI sensor were evaluated. Calibration data sets obtained using the soil-leaf-canopy radiative transfer model; a state-of-the-art airborne imaging spectrometer Airborne Prism Experiment (APEX); and univariate and multivariate regression models were considered for SRF cross-sensor calibration. For AVHRR9 and VGT1, reflectances in the red spectral region differed more than 30% from Sentinel-2 reflectances. These differences translated in NDVI deviations of up to 10%. The developed SRF cross-sensor calibration method reduced the differences by factors up to 6, 3, and 7 for red, NIR, and NDVI values, respectively. All but AVHRR9 have been found to be cross-calibrated to within 5% differences for reflectances and NDVI values. The present work is considered as part of a broader harmonization effort aimed at preparing for the integration of Sentinel-2 MSI data with existing historical data records and product time series.

Long-term vegetation monitoring for different habitats in floodplains

Long-term vegetation monitoring for different habitats in floodplains

Analysis of the Scaling Effects in the Area-Averaged Fraction of Vegetation Cover Retrieved Using an NDVI-Isoline-Based Linear Mixture Model

The spectral unmixing of a linear mixture model (LMM) with Normalized Difference Vegetation Index (NDVI) constraints was performed to estimate the fraction of vegetation cover (FVC) over the earth’s surface in an effort to facilitate long-term surface vegetation monitoring using a set of environmental satellites. Although the integrated use of multiple sensors improves the spatial and temporal quality of the data sets, area-averaged FVC values obtained using an LMM-based algorithm suffer from systematic biases caused by differences in the spatial resolutions of the sensors, known as scaling effects. The objective of this study is to investigate the scaling effects in area-averaged FVC values using analytical approaches by focusing on the monotonic behavior of the scaling effects as a function of the spatial resolution. The analysis was conducted based on a resolution transformation model introduced recently by the authors in the accompanying paper (Obata et al., 2012). The maximum value of the scaling effects present in FVC values was derived analytically and validated numerically. A series of derivations identified the error bounds (inherent uncertainties) of the averaged FVC values caused by the scaling effect. The results indicate a fundamental difference between the NDVI and the retrieved FVC from NDVI, which should be noted for accuracy improvement of long-term observation datasets.

Suitability of methods for recording species numbers and cover in alpine long-term vegetation monitoring

Methods of vegetation recording – subplot frequency, point-framing and visual cover estimation – were assessed in terms of their usefulness in high alpine environments, with a focus on their suitability for long-term monitoring programmes. Two of the methods for estimating cover (point-framing and visual estimation) were comparable only for covers above 0.7% in 1 m2. For detecting the exact species number, point-framing was unsuitable while the other two methods yielded similar results. The time taken to complete a quadrat varied for each method, with point-framing being the quickest and most unaffected by species number or vegetation cover. When trying to detect change over time and conducting long-term vegetation monitoring, the exact species number of a plot, and similarly the cover of rare and small species are especially important. We suggest therefore that, despite its drawbacks, visual estimation is the most suitable method in alpine vegetation, because it gives a reliable species number, the cover estimation is comparable to point-framing, and it takes less time than subplot frequency.

A comparison of methods to assess long-term changes in Sonoran Desert vegetation

Knowledge about the condition of vegetation cover and composition is critical for assessing the structure and function of ecosystems. To effectively quantify the impacts of a rapidly changing environment, methods to track long-term trends of vegetation must be precise, repeatable, and time- and cost-efficient. Measuring vegetation cover and composition in arid and semiarid regions is especially challenging because vegetation is typically sparse, discontinuous, and individual plants are widely spaced. To meet the goal of long-term vegetation monitoring in the Sonoran Desert and other arid and semiarid regions, we determined how estimates of plant species, total vegetation, and soil cover obtained using a widely-implemented monitoring protocol compared to a more time- and resource-intensive plant census. We also assessed how well this protocol tracked changes in cover through 82 years compared to the plant census. Results from the monitoring protocol were comparable to those from the plant census, despite low and variable plant species cover. Importantly, this monitoring protocol could be used as a rapid, “off-the shelf” tool for assessing land degradation (or desertification) in arid and semiarid ecosystems.

The impact of African elephants on Acacia tortilis woodland in northern Gonarezhou National Park, Zimbabwe

We investigated the impact of African elephants ( Loxodonta africana) on the structure and composition of Acacia tortilis woodland in northern Gonarezhou National Park, southeast Zimbabwe. A. tortilis woodland was stratified into high, medium and low elephant utilisation categories based on evidence of elephant habitat use as determined through dung-count surveys in relation to distance of woodland patches from perennial and natural surface water sources. The following variables were recorded in each study plot: tree height, species name, number of species, plant damage, basal circumference and number of stems per plant. A total of 824 woody plants and 26 woody species were recorded from the sampled A. tortilis woodland patches. Mean tree densities, basal areas, tree heights and species diversity were lower in areas with medium and high elephant utilisation as compared to low elephant utilisation areas. Plants damaged by elephants increased with increasing elephant utilisation. The study findings suggest that A. tortilis woodland is gradually being transformed into an open woodland. We recommended that protected area management in arid and semi-arid areas should consider (i) formulating clear thresholds of potential concern to allow for the conservation of sensitive woodlands such as A. tortilis woodlands and (ii) establishing long-term vegetation monitoring programmes.

Power analysis for trend in ordinal cover classes: implications for long-term vegetation monitoring

Question: We provide a method to calculate the power of ordinal regression models for detecting temporal trends in plant abundance measured as ordinal cover classes. Does power depend on the shape of the unobserved (latent) distribution of percentage cover? How do cover class schemes that differ in the number of categories affect power? Methods: We simulated cover class data by “cutting-up” a continuous logit-beta distributed variable using 7-point and 15-point cover classification schemes. We used Monte Carlo simulation to estimate power for detecting trends with two ordinal models, proportional odds logistic regression (POM) and logistic regression with cover classes re-binned into two categories, a model we term an assessment point model (APM). We include a model fit to the logit-transformed percentage cover data for comparison, which is a latent model. Results: The POM had equal or higher power compared to the APM and latent model, but power varied in complex ways as a function of the assumed latent beta distribution. We discovered that if the latent distribution is skewed, a cover class scheme with more categories might yield higher power to detect trend. Conclusions: Our power analysis method maintains the connection between the observed ordinal cover classes and the unmeasured (latent) percentage cover variable, allowing for a biologically meaningful trend to be defined on the percentage cover scale. Both the shape of the latent beta distribution and the alternative hypothesis should be considered carefully when determining sample size requirements for long-term vegetation monitoring using cover class measurements.

English

Annual bromes, primarily cheatgrass (Bromus tectorum) and Japanese brome (Bromus japonicus) are Eurasian winter annual plants that have come to be considered invasive. As such they are not included purposely in seed mixes used for mine reclamation. Examination of long-term vegetation monitoring data from reclaimed and reference areas at the Big Sky Mine in Rosebud County, MT offer insight into the dynamics of the presence of these weeds in a Northern Great Plains setting. Over the past 22 years, annual brome cover as a percent of total vegetation cover in the native open ponderosa pine (Pinus ponderosa) woodland vegetation at the Big Sky Mine has varied from as low as 0.3% in 2002 to as high as 50.7% in 1991. In reclaimed areas over the same period, annual bromes ranged from as little as 1.5 % to as much as 25.1 % of total vegetation cover. As of 2008 Native Reference Area vegetation was 37.0% annual bromes while reclaimed areas had declined to 6.5% annual bromes. Biomass production in reclaimed areas has exceeded reference area levels by 50 to 75% on most years. Precipitation in these adjacent areas can be presumed to have been very similar and grazing of both areas has been light to non-existent over the period. These data suggest that strong perennial herbaceous growth suppresses annual brome abundance especially during periods favorable precipitation. Native area vegetation periodically experiences outbreaks of annual bromes as drought stresses increase and then annual bromes decline as the competitive strength of the native perennials returns. High abundance of annual bromes is a symptom of reduced or lagging competitive strength of perennial plants: it is suggested that at least in the Northern Great Plains, annual bromes constitute a litmus test for community competitive strength, and are not of themselves a conquering invasion. Additional Keywords: Invasibility, reclamation biomass production, cheatgrass, downy brome, Japanese brome, invasive plants, cycles of invasions.

Influence of biotic and abiotic factors on annual aboveground biomass of an intermediate coastal marsh

Annual production of vegetation is an important indicator of various ecosystem processes in coastal marshes; many factors, both biotic and abiotic, can influence production of aboveground biomass. Using a 14-year data set, we evaluated the relative influence of 38 biotic and abiotic factors on annual aboveground biomass of an intermediate coastal marsh on the upper Gulf Coast of Texas. We used visual obstruction (VO) measurements as a surrogate variable in a prediction model to estimate available aboveground biomass in the marsh. Available biomass was greatest (3.34 kg/m 2 ) when sampling site was flooded. Plant growth form, type of animal present, and composition of the ground cover influenced biomass of the marsh. Presence of insects was related to biomass (regression beta weight 5 0.28), uniquely accounting for 7.6% of the incremental variance in biomass. The presence of moderate amounts of litter was also related to available biomass (beta weight 5 0.86). Soil capping had little or no influence on aboveground biomass. Implementing standard protocols for long-term vegetation monitoring can be cost and time intensive. Our results suggest quantitative measurement of VO and qualitative observation of few variables (standing water, insects, and litter) measured annually can yield a reasonable assessment of aboveground biomass of intermediate coastal marshes.

Recovery stages over long-term monitoring of the intertidal vegetation in the ‘Abra de Bilbao’ area and on the adjacent coast (N. Spain)

Few studies have documented the recovery of phytobenthic marine assemblages following the reduction of long-standing sewage discharges. This paper reports on the main changes in intertidal macroalgal communities after the gradual application from 1984 to 2006 of a sewerage plan for the metropolitan area of Bilbao. Sampling sites along a pollution gradient were surveyed eight times during the course of the above period. Improvements in water quality were followed by noticeable changes in species composition and vegetation structure. Species richness significantly increased throughout the study area, while algal cover only increased at the most degraded sites. Pollution removal promoted the development of morphologically more complex species. Intertidal vegetation at the degraded sites became progressively more similar to that at the reference site. Five recovery stages discriminated by different species (SIMPER routine) were characterized from ordination (MDS) analyses: (i) extremely degraded–Gelidium pusillum is the most abundant species which is accompanied by Bachelotia antillarum at the low intertidal level (0.75 m); (ii) heavily degraded–Gelidium pusillum remains dominant and accompanied by Caulacanthus ustulatus at the high intertidal level (1.4 m); (iii) moderately degraded–Corallina elongata becomes dominant, C. ustulatus remains abundant at the high level; (iv) slightly degraded–C. elongata remains dominant in both tidal levels, Chondracanthus acicularis and Lithophyllum incrustans are abundant at the high level, whereas the latter, Pterosiphonia complanata and Stypocaulon scoparium become abundant at the low level; (v) reference stage–Lithophyllum incrustans and Laurencia obtusa are abundant together with C. elongata at the high level, whereas Stypocaulon scoparium dominates the low level, with Bifurcaria bifurcata, Jania rubens and Cystoseira tamariscifolia as abundant species. Thus, this study reveals that phytobenthic communities are useful indicators of water quality and provide real data that contribute to the assessment of the ecological status of rocky open shores on the Basque coast.

IMPACTS OF AN EXOTIC DISEASE AND VEGETATION CHANGE ON FOLIAR CALCIUM CYCLING IN APPALACHIAN FORESTS

Because of the high calcium content of its foliage, Cornus florida (flowering dogwood) has been described as a calcium "pump" that draws calcium from deeper mineral soil and enriches surface soil horizons. However, over the last two decades an exotic fungal disease (dogwood anthracnose, Discula destructiva) has decimated populations of this once-common understory species. Its loss, combined with forest stand development, could alter intra-stand calcium cycling. We used data from long-term vegetation monitoring plots to examine the ecological role of C. florida in calcium cycling and to identify changes in annual foliar calcium cycling over a 20-year period between two sampling intervals, 1977-1979 (preanthracnose) and 1995-2000 (post-anthracnose). Published equations were used to estimate foliar biomass per species for five forest types: alluvial, typic cove, acid cove, oak-hickory, and oak-pine. Calcium concentrations derived from foliage samples were used to estimate annual foliar calcium production per species for understory woody stems (<20 cm dbh) and total foliar calcium production for overstory stems (> or =20 cm dbh). At a given level of soil calcium availability, C. florida foliage contained greater concentrations of calcium than three other dominant understory species (Tsuga canadensis, Acer rubrum, and Rhododendron maximum). Between 1977-1979 and 1995-2000, the annual calcium contributions of understory woody vegetation declined across all forest types, ranging from 26% in oak-pine stands to 49% in acid coves. Loss of C. florida was responsible for only 13% of this decline in oak-pine stands, but accounted for 96% of the decline in typic coves. In oak-hickory and oak-pine stands, we observed large increases in the foliar biomass of T. canadensis, a species whose calcium-poor foliage increases soil acidity. Increases in overstory foliar biomass and calcium offset understory losses in three forest types (alluvial, typic coves, and oak-pine) but not in oak-hickory and acid cove stands. Overall, calcium cycling in oak-hickory stands was more negatively affected by the loss of C. florida than the other forest types. Oak-hickory forests comprise over a third of the total forest cover in the eastern United States, and decreases in annual calcium cycling could have cascading effects on forest biota.

Long-term vegetation monitoring with NDVI in a diverse semi-arid setting, central New Mexico, USA

Time-series of normalized difference vegetation index (NDVI) are shown to capture essential features of seasonal and inter-annual vegetation variability at six nearby yet distinct vegetation communities in semi-arid New Mexico, USA NDVI values tend to follow a uniform order across communities, related directly to local vegetation. All communities exhibit a bimodal growing season on average, with peaks in springtime and summer. NDVI fluctuations are more spatially uniform in spring than in summer. NDVI variability corresponds to precipitation variability from the North American monsoon and El Niño-Southern Oscillation, and shows agreement with regional ground measurements.

Restoration ecology of riverine wetlands: A 5-year post-operation survey on the Rhône River, France

Bibliographical study of articles published in scientific journals over the last 10 years, and of books published over the last 20 years, reveals a clear increase in the number of publications dealing with ecological engineering, particularly on aquatic ecosystems, which today are becoming a major topic. The concept of ecological restoration must be clearly defined scientifically and include adequate pre- and post-restoration monitoring of various performance indicators, to allow for restoration, evaluation and increase its success. A restoration experiment was carried out in a former channel of the Rhône River according to a scientifically based decision framework. Long-term monitoring of aquatic vegetation (17 years of data) on two former channels (reference and restored ecosystem) clearly demonstrated human impacts on aquatic ecosystems. A channel exhibiting rapid terrestrialization and eutrophication processes after completion of a hydroelectric scheme construction was restored. In keeping with the hypothesis, the increase in groundwater supply led the restored ecosystem to return to a less advanced and self-sustainable successional stage, whereas vegetation monitoring in the reference channel did not show significant changes over this 17-year of period, supporting long-term studies to determine the effects of restoration on the biota.

Data pre‐processing: Stratospheric aerosol perturbing effect on the remote sensing of vegetation: Correction method for the composite NDVI after the Pinatubo eruption

Stratospheric aerosols produced by the eruption of Mount Pinatubo in the Philippines (6 June, 1991) had a detectable effect on NOAA AVHRR data. Following the eruption, a longitudinally homogeneous dust layer was observed between 20°N and 20°S. The largest optical thickness observed for the dust layer was 0.4–0.6 at 0.5 pm. The amount of aerosols produced by Mount Pinatubo was two to three times greater than that produced by El Chichon and the Stratospheric Aerosol and Gas Experiment (SAGE) on‐board the Earth Radiation Budget Experiment was not able to give quantitative estimate of aerosol optical thickness because of saturation problem. The monthly composite Normalized Difference Vegetation Index (NDVI) (generally bounded between ‐0.1 and 0.6) has systematically decreased by approximately 0.15 two months after the eruption. Such atmospheric effect has never been observed on composite product and is related to the persistence and spatial extent of the aerosol layer causing the composite technique to fail. Therefore, long term monitoring of vegetation using the NDVI necessitates correction of the effect of stratospheric aerosols. In this paper we present an operational stratospheric aerosol correction scheme adopted by the Laboratory for Terrestrial Physics, NASA/GSFC. The stratospheric aerosol distribution is assumed to be only variable with latitude. Each 9 days the latitudinal distribution of the optical thickness is computed by inverting radiances observed in AVHRR channel 1 (0.63 μm) and channel 2 (0.83 μm) over the Pacific Ocean. This radiance data set is used to check the validity of model used for inversion by checking consistency of the optical thickness deduced from each channel as well as optical thickness deduced from different scattering angles. Using the optical thickness profile previously computed and radiative transfer code assuming lambertian boundary condition, each pixel of channel 1 and 2 are corrected prior to computation of NDVI. Comparison between corrected, not corrected, and years prior to Pinatubo eruption (1989, 1990) NDVI composite, shows the necessity and the accuracy of the operational correction scheme.

Long-Term Vegetation Monitoring in the Serengeti National Park, Tanzania

(1) Several investigators have suggested that portions of the perennial grasslands of the Serengeti plains have recently been converted to annual-grass and shrub-dominated communities due to overgrazing and disturbances by wildebeest, which have increased five-fold in population since 1961. Study sites that were described and mapped in the 1960s and 1970s were revisited in 1982 and their species compositions and community patterns compared to the earlier descriptions. (2) No changes in species composition were found in any of the communities. Vegetational mosaic patterns in aerial photographic plots had not visibly changed in size, shape, or position over a 10-year period. (3) The Zurich-Montpellier method used to describe the vegetation of several sites in 1972 was inappropriate for long-term vegetation monitoring. It is suggested that, in future, vegetational changes be monitored by recording the percentage cover of species in small, permanently marked plots. (4) No evidence of range deterioration was found in the Serengeti grasslands.